转贴一篇,jquery实现的twitter/facebook样式的下拉菜单,正好要用...

The HTML

<div id="menu1"><div class="relative">
        <a href="/demos" title="Popular MooTools Tutorials" id="dd1" class="dropdown" style="width:170px;text-decoration:none;"><span>Menu 1</span></a>
        <div id="dropdown1" class="dropdown-menu">
                <a href="/about-david-walsh" title="Learn a bit about me.">About Me</a>
                <a href="/page/1" title="The David Walsh Blog">Blog</a>
                <a href="/chat" title="#davidwalshblog IRC Chat">Chat</a>
                <a href="/contact" title="Contact David Walsh">Contact Me</a>
                <a href="/demos" title="CSS, PHP, jQuery, MooTools Demos">Demos &amp; Downloads</a>
                <a href="/js" title="ScrollSpy, Lazyload, Overlay, Context Menu">MooTools Plugins</a>
                <a href="/network" title="David Walsh Blog, Script &amp; Style, Band Website Template, Wynq">Network</a>
                <a href="/web-development-tools" title="JS, CSS Compression">Web Dev Tools</a>
        </div>
</div></div>

<div id="menu2"><div class="relative">
        <a href="/demos" title="Popular MooTools Tutorials" id="dd2" class="dropdown" rel="dropdown2" style="width:170px;text-decoration:none;"><span>Menu 2</span></a>
        <div id="dropdown2" class="dropdown-menu">
                <p>Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.</p>
        </div>
</div></div>

A series of DIVS wrapping a link (the dropdown “trigger”) and a DIV containing the menu items.

The CSS

/* dropdowns: general */
a.dropdown { background: #88bbd4; padding: 4px 6px 6px; text-decoration: none; font-weight: bold; color: #fff; -webkit-border-radius: 4px; -moz-border-radius: 4px; border-radius: 4px; }
a.dropdown:hover { background: #59b; }
a.dropdown { position: relative; margin-left: 3px; }
a.dropdown span { background-image: url(toggle_down_light.png); background-repeat: no-repeat; background-position: 100% 50%; padding: 4px 16px 6px 0; }
a.dropdown.dropdown-active { color:#59b; background-color:#ddeef6; }
a.dropdown.dropdown-active span { background:url(toggle_up_dark.png) 100% 50% no-repeat; }
.dropdown-menu  { background:#ddeef6; padding:7px 12px; position:absolute; top:16px; right:0; display:none; z-index:5000; -moz-border-radius-topleft: 5px; -moz-border-radius-bottomleft: 5px; -moz-border-radius-bottomright: 5px; -webkit-border-top-left-radius: 5px; -webkit-border-bottom-left-radius: 5px; -webkit-border-bottom-right-radius: 5px; }
        .dropdown-menu p { font-size:11px; }
.dropdown-menu a:link, .dropdown-menu a:visited { font-weight:bold; color:#59b; text-decoration:none; line- }
.dropdown-menu a:active, .dropdown-menu a:hover { color:#555; }

                        * html .dropdown-menu { top:28px; }
                        *+ html .dropdown-menu { top:28px; }

/* dropdowns: specific */
#menu1                  { float:left; margin-right:20px; }
        #dropdown1      { width:150px; }
        #dropdown1 a    { display:block; }
#menu2                  { float:left; }
        #dropdown2      { width:150px; font-size:11px; }
.relative               { position:relative; }

There’s a lot of CSS involved but most of it is simple visual styling as opposed to styling for JavaScript’s sake. Do, however, note where relative and absolute positioning is used. The outermost DIV may be positioned absolutely if you’d like. Also note that I’m not doing anything to accommodate for rounded corners in IE — I recommend DD_Roundies for that.

The jQuery JavaScript

$(document).ready(function() {
        /* for keeping track of what's "open" */
        var activeClass = 'dropdown-active', showingDropdown, showingMenu, showingParent;
        /* hides the current menu */
        var hideMenu = function() {
                if(showingDropdown) {
                        showingDropdown.removeClass(activeClass);
                        showingMenu.hide();
                }
        };
        
        /* recurse through dropdown menus */
        $('.dropdown').each(function() {
                /* track elements: menu, parent */
                var dropdown = $(this);
                var menu = dropdown.next('div.dropdown-menu'), parent = dropdown.parent();
                /* function that shows THIS menu */
                var showMenu = function() {
                        hideMenu();
                        showingDropdown = dropdown.addClass('dropdown-active');
                        showingMenu = menu.show();
                        showingParent = parent;
                };
                /* function to show menu when clicked */
                dropdown.bind('click',function(e) {
                        if(e) e.stopPropagation();
                        if(e) e.preventDefault();
                        showMenu();
                });
                /* function to show menu when someone tabs to the box */
                dropdown.bind('focus',function() {
                        showMenu();
                });
        });
        
        /* hide when clicked outside */
        $(document.body).bind('click',function(e) {
                if(showingParent) {
                        var parentElement = showingParent[0];
                        if(!$.contains(parentElement,e.target) || !parentElement == e.target) {
                                hideMenu();
                        }
                }
        });
});

I’ve commented to the code to illustrate what each block does. In a nutshell:

• I create placeholder variables which will keep track of the current menu, dropdown, and parent for the opened menu. This functionality is only included because I don’t want more than one menu to be open at a time.
• I create a function that hides the current menu — this can be used from anywhere within the closure.
• I cycle through each dropdown and add events to relevant elements to show and hide menus.
• I add an event to the body to close the current menu if the user clicks outside of the menu.

That’s it!

原文地址：http://davidwalsh.name/twitter-dropdown-jquery。